In hydraulically actuated fuel injection systems, a control valve body is provided with a valve system having grooves or orifices that allow fluid communication between working ports, high pressure ports, and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid that is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current configurations, an injector driver circuit delivers a current or voltage to an open coil solenoid. The magnetic force generated in the open coil solenoid will shift an armature (spool) into the open position so as to align grooves of the control valve body with grooves in the armature. The alignment of the grooves permits the working fluid to flow into an intensifier chamber. This alignment is permitted for the requested duration of fuel injection, after which the injector driver circuit delivers a current/voltage to the close coil solenoid which shifts the armature to the close position and stops the fluid flow due to the grooves being misaligned. Injection duration is from the time the alignment of the grooves occurs in the open motion of the armature to the time the groove alignment is lost in the close motion of the armature.
Due to armature or spool surface wear and other magnetic effects, the armature motion from the open position to the close position becomes faster over injector operation time. This results in loss of grove alignment in the close motion of the armature earlier than expected, leading to lower injection duration which in turn results in lower fuel delivery than expected.
Thus, there is a need to compensate for the lost fuel delivery/engine power by ensuring that the full requested injection duration is achieved.